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UNITED STATES DEPARTMENT OF THE INTERIOR

GEOLOGY AND BIOLOGY OF NORTH ATLANTIC DEEP-SEA CORES

SUMMARY, FOREWORD, AND GENERAL INTRODUCTION

PART 1. LITHOLOGY AND GEOLOGIC INTERPRETATIONS

PART 2. FORAMINIFERA

GEOLOGICAL SURVEY PROFESSIONAL PAPER 196-A

UNITED STATES DEPARTMENT OF THE INTERIOR Harold L. Ickes, Secretary

GEOLOGICAL SURVEY W. C. Mendenhall, Director

Professional Paper 196-A

GEOLOGY AND BIOLOGY OF

NORTH ATLANTIC DEEP-SEA CORESBETWEEN NEWFOUNDLAND AND IRELAND

SUMMARY OF THE REPORT

FOREWORD, BY C. S. PIGGOT

GENERAL INTRODUCTION, BY W. H. BRADLEY

PART 1. LITHOLOGY AND GEOLOGIC INTERPRETATIONSBy M. N. BRAMLETTE AND W. H. BRADLEY

PART 2. FORAMINIFERA

By JOSEPH A. CUSHMAN AND LLOYD G. HENBEST

UNITED STATES

GOVERNMENT PRINTING OFFICE

WASHINGTON : 1940

For eale by the Superintendent of Documents, Washington, D. C. ------- Price 30 cents

CONTENTS

Summary of the report-_____________________________Foreword, by C. S. Piggot___________________________General introduction, by W. H. Bradley.______________

Significance of the investigation._________________Location of the core stations.____________________Personnel and composition of the report___________Methods of sampling and examination___________

Part 1. Lithology and geologic interpretations, by M. N. Bramlette and W. H. Bradley. _____________________

Examination and analysis of samples...___________Acknowledgments__ _ _ _________________________Presentation of data.___________________________Stratigraphic units______________________________

Volcanic ash zones._________________________Glacial marine deposits__--__-_---___--_____-

Correlation of zones represented in the cores.______Interpretation of the glacial marine succession______

Sources of detritus._________________________Temperature of the ocean, as indicated by the

deposits.________________________________Interpretation of the glacial marine zones in

terms of stages or substages of the Pleistocene- Post-glacial climatic changes.____„___________

Rate of deep-sea sedimentation.__________________

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XIII

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Part 1. Lithology and geologic interpretation—Contd. Evidence of bottom currents.____________________Submarine slumping.___________________________Carbonate content of the sediments_-_____. _______Sulphates. _____________________________________Siliceous organisms_____-______-__----____-_---Role of mud-feeding organisms___________________Mineralogy of the clastic sediments.______________Spectroscopic tests._____________________________Porosity of the sediments.-____.-__._-_________-.Mechanical analyses.______________-__-______..--Basaltic pyroclastics and their alteration___________Volcanic rock in core ll______________-_-___-_--_Basaltic mud in core 10________________________

Part 2. Foraminifera, by Joseph A. Cushman and Lloyd G. Henbest.________________________________________

Preparation of samples_____________-_______-__-_Acknowledgments. __ _ _________________________Distribution in the cores and list of species________Pelagic Foraminifera-___________________________Bottom-living Foraminifera___-_--__-.__-____-___Bathymetric distribution._______________________Temperature indications-________________________Age and correlation__________________________.__

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ILLUSTRATIONS

Page PLATE 1. Bathymetric chart of a part of the North Atlantic Ocean showing the location of the core stations._______________ xv

2. Longitudinal sections of the air-dried cores---_--------__-----_-------_--------_-------------------------- xv3. Diagram showing the lithology and correlation of lithologic zones in the cores___-__________-_____----_--_-_-_-.. 44. Diagram showing Cushman and Henbest's interpretation of water temperatures indicated by the pelagic Foram-

inifera- __-___-______„___-__________--_-__________-___-__-_______--__-_______--_---------.----------_ 45. A, Fecal pellets or filled borings in basaltic mud; B, Fecal pellets or filled borings in foraminiferal marl___________ 326. Standard pyramid diagram showing the size distribution, kinds of organisms, and mineral particles in four types of

sediment_ __-____________________________-___-________-____-___-___-_--_---------___--_----------- 327. A, Zeolite crystals in clayey rock; B, Upper surface of the clayey rock, which is interpreted as an alteration product

of basaltic lava; C, Palagonite rims surrounding fragments of unaltered basaltic glass; D, Foraminifera shells replaced by a zeolite.____________________________-____-_______--___---_-_-----_---_----------------- 32

8-10. Foraminifera from the North Atlantic deep-sea cores____________-__________-_____---_--,_---_--__--_--_---_ 51-54FIGURE 1. Profile across the North Atlantic Ocean bottom along the line of the numbered core stations-________-_--____--_ xiv

2. Diagram showing the inferred relations of glacial marine and nonglacial sediments____________________________ 83. Diagram showing three interpretations of the glacial marine zones in terms of stages and substages of the Pleisto-

cene.---..---_--_---_-_-__-__------__-_---__--------_--_-----_---------------.--------------------- 104. Curve showing amplitude of solar radiation changes during the past 300,000 years___-__________--_---_------_ 125. Graph showing the CaO-CO2 ratios of core samples in relation to the CaO-CO2 ratio of pure calcite_ _____________ 176. Diagram showing distribution of volcanic ash shards in sediments._______-______-___-__________--_--_----_-- 227. Dehydration curves of basaltic mud from core 10, a red clay from the Pacific Ocean, and typical halloysite and

montmorillonite from clay deposits in the United States_____________-____-_________--_--_-_-_-____------ 248. Relation of calculated original porosity of blue mud in core 3 to depth below top of core _______________-_-_----- 279. Sketch of the two halves of the top part of core 3 showing differential shrinkage.____--______-___-_-__-.-_---_ 28

10. Curves showing size distribution of organisms and mineral particles in blue mud, a gravelly foraminiferal marl,globigerina ooze, and clay________-___-_-_________-___--__-___-_-----_-_----_--------__-_------------ 29

11-21. Charts showing distribution and temperature significance of Foraminifera in the cores........________________ -- 36-45in

IV CONTEXTS

TABLES

Page

TABLE 1. Geographic location, length of cores, and depth of the water from which they were taken___.----_-_----------- xiv2. Grain-size distribution in sample B-53 from core 5 and approximate composition________________-_--_----_-_- 153. Distribution of magnesium carbonate within cores 3 to 13______-_______-_--_-__--__----_----_------------- 194. Lime-magnesia ratios of the samples shown in table 3_ _---._--__---------_----.----_--.-----_---------------- 215. Grain and lump density and porosity of dried mud from cores 3 and 10, ard calculated original porosity _,.___________ 276. Relative oxidation of iron in fresh and altered submarine basaltic glass-______________.________-_____-__--_--- 317. Analyses of mud from core 10 (sample W-15) and oceanic red cla3'S_____-__-__-_-____-___---_ _______________ 33

OUTLINE OF THE COMPLETE REPORT

Foreword, by C. S. Piggot.General introduction, by W. H. Bradley.PART 1. Lithology and geologic interpretations, by M. N. Bramlette and W. H. Bradley.

2. Foraminifera, by Joseph A. Cushman and Lloyd G. Henbest.3. Diatomaceae, by Kenreth E. Lohnaan.4. Ostracoda, by Willis L. Tressler.5. Mollusca, by Harald A. Render.6. Echinodermata, by Austin H. Clark.7. Miscellaneous fossils and significance of faunal distribution, by Lloyd G. Henbest.8. Organic matter content, by Parker D. Trask, H. Whitman Patnode, Jesse LeRoy Stimson, and John R. Gay.9. Selenium content and chemical analyses, by Glen Edgington and H. G. Byers.

SUMMARY OF THE REPORT

In May and June 1936 Dr. C. S. Piggot of the Geophysical Laboratory, Carnegie Institution of Washington, took a series of 11 deep-sea cores in the North Atlantic Ocean between the Newfoundland banks and the banks off the Irish coast. These cores were taken from the Western Union Telegraph Co.'s cable ship Lord Kelvin with the explosive type of sounding device which Dr. Piggot designed. In the fall of that year he invited a group of geologists of the United States Geological Survey to study the cores and prepare a report. Biologists of the United States National Museum, the University of Buffalo, and chem- ists of the United States Department of Agriculture cooperated in the investigation and contributed to the report.

The westernmost core of the series (No. 3) was taken in the blue mud zone, but all the others were taken in parts of the ocean where the bottom is blanketed with globigerina ooze. The shortest cores are No. 8, taken on the mid-Atlantic ridge in 1,280 meters of water, and No. 11, taken where the core bit struck volcanic rock. The cores range in length from 0.34 to 2.93 meters and average 2.35 meters. They were taken at depths ranging from 1,280 to 4,820 meters.

Lithology and geologic interpretations.—In about 20 representative samples from each core the percentages of calcium carbonate, clay and silt, and sand were determined and plotted, and the relative abundance of Foraminifera, coccoliths, and diatoms was estimated. Material between these guide samples was examined microscopically, especially in certain critical zones.

Two zones were noted in which silicic volcanic ash (refractive index near 1.51) is common. The upper ash zone was found in all the cores except No. 11, but the lower one was found only in the lower part of cores 4 to 7. In core 3 the upper ash zone is represented by shards scattered very sparsely all through the core, as this core, despite its length of 2.82 meters, apparently did not reach the bottom of the ash zone. The upper ash zone, together with other adjacent lithologic zones, serves to correlate the cores, and the lower ash zone, found west of the mid-Atlantic ridge, helps to confirm the correlation.

Besides the zones of volcanic ash four other zones distinctive in lithologic character were found. These zones are characterized by a relative abundance of sand and pebbles, by a smaller percentage of calcium carbonate, and by a sparsity of Foramini- fera and coccoliths. They are distinctive also in texture. The pebbles are subrounded to angular and include a wide variety of rock types—sandstone, gneiss, soft shale, and limestone—of which limestone is the most common. Some of the pebbles are as much as 2 centimeters across. These zones are interpreted as glacial marine deposits formed during the Pleistocene glacial epoch, when continental glaciers were eroding the land. Drift ice from the continental glaciers apparently transported considera- able quantities of rock debris far out into the ocean basin.

Between the glacial marine zones found in the North Atlantic cores the sediments consist chiefly of foraminiferal ooze or marl, much like that which is forming today in the same area.

The uppermost glacial marine zone is represented in all the cores except Nos. 3 and 11 and lies just below the upper volcanic ash zone. In cores 4 to 7 the glacial zones are relatively thin and are spaced at approximately equal intervals; between the third and fourth glacial zones (in descending order) is the lower volcanic ash. East of the mid-Atlantic ridge only the uppermost glacial

zone has been identified. Other glacial marine deposits are recognizable but their correlation is less certain.

Three interpretations are offered as possible explanations of the four glacial marine zones. The first is that each glacial marine zone represents a distinct glacial stage of the Pleistocene and that each zone of foraminiferal marl separating two glacial marine zones represents an interglacial stage. This interpretation seems least probable of the three. The second interpretation is that the upper two glacial marine zones and the intervening sediment may correspond to the bipartite Wisconsin stage, whereas the lower two represent distinct glacial stages of the Pleistocene separated from each other and from the zone representing the Wisconsin stage by sediments that, represent interglacial epochs no greater in length than postglacial time. This interpretation seems to imply too short a time for most of the Pleistocene epoch. The third interpretation, which is favored by the authors, is that each of the four glacial marine zones represents only a substage of the Wisconsin stage. This implies that the North Atlantic at approximately 50° north latitude for comparatively long periods of time alternately contained an abundance of drift ice and then was quite, or nearly, free of ice, while on land a continental ice sheet persisted, though it alternately waned and grew.

In the four cores in which the postglacial sediments are thickest the pelagic Foraminifera, according to Cushman and Henbest, reveal an interesting condition. These organisms indicate that during the middle part of the postglacial interval the temperature of the surface water in that part of the North Atlantic was somewhat higher than prevails today.

On the assumptions that the top of the uppermost glacial marine zone represents the beginning of the postglacial epoch as defined by Antevs, and that this was probably as much as 9,000 years ago, the postglacial sediment in these cores accumulated at a rate of about 1 centimeter in 265 years; but, because the sea probably cleared of detritus-laden drift ice long before the land in the same latitude was cleared of the retreating continental ice sheet, the average rate of accumulation may have been as low as 1 centimeter in 500 years.

Coarse-grained sediment on the tops of ridges and fine-grained sediment in the deeper basins indicate that currents move across these ridges with sufficient velocity to winnow out the finer particles and sweep them into deeper basins beyond.

The fact that the glass shards in the volcanic ash zones have been reworked and distributed without any gradation in size through many centimeters of the overlying sediments leads us to believe that mud-feeding animals are continually working over these shards and other particles of sand and silt so that they are redistributed at successively higher levels. The shards and other particles may also be reworked by gentle bottom currents that move the material from mounds and ridges on the sea floor and drift it about over the adjacent flatter areas.

Several layers in the cores are sharply set off by the coarser grain size of the sediment or by a regular gradation in grain size from coarsest at the base to fine at the top. These may be a result of submarine slumping.

The term globigerina ooze is used loosely in this report to designate sediment, half or more than half of which, by weight, consists of Foraminifera. This usage accords more closely with

VII

VIII SUMMARY OF THE REPORT

the usage adopted by Correns in the Meteor reports than with the usage of Murray and Chumley in the Challenger reports, which was based solely on the carbonate content. Limy muds containing a lesser but still conspicuous number of Foraminifera are referred to as foraminiferal marl. The carbonate content of the globigerina ooze in these cores ranges from 46.6 to 90.3 percent and averages 68.2 percent. In 191 samples representing all the lithologic types, the carbonate content ranges from 10.0 to 90.3 percent and averages 41.3 percent. Coccoliths are abundant in many parts of the cores, but by reason of their small size they rarely make up as much as 10 percent of the sediment. Pteropods are rather numerous in parts of the cores taken on the mid-Atlantic ridge and on the continental slope off the Irish coast.

Most of the calcium carbonate in these sediments consists of the tests and comminuted fragments of calcareous organisms. The finest particles of carbonate are of indeterminate origin, but their irregular shape and range in size suggest that they are largely the finest debris of the comminuted organisms rather than a chemical precipitate. Clusters or rosettes of calcium carbonate crystals were found in many samples, but they are not abundant. They evidently formed in the mud on the sea floor.

No conclusive evidence of an increase in magnesium carbonate with depth was found, though some of the data suggest it. The magnesium carbonate is somewhat more abundant in the glacial marine zones than elsewhere, but its concentration in those zones is probably accounted for by the presence of clastic grains and pebbles of dolomite.

Diatom frustules, radiolarian skeletons, and sponge spicules are the most common siliceous organic remains found in the cores, and these generally form less than 1 percent of the sediment. One notable exception is the sediment in the middle part of core 9, just east of the mid-Atlantic ridge, which contains 50 percent or more of diatoms.

Ellipsoidal and elongate or cylindrical pellets that appear to be fecal pellets are plentiful in the mud at the tops of cores 10 and 12, taken in the eastern part of the North Atlantic, but were not found elsewhere. No attempt was made to identify them further.

The sand-size material showed no marked variation in the mineral composition of the clastic grains at different horizons within individual cores and no conspicuous lateral variation from core to core. The mineral grains in the sand-size portions were not separated into light and heavy fractions, but simple inspection showed that grains of the heavy minerals are somewhat more common in the glacial marine deposits than elsewhere. Well-rounded sand grains are sparsely scattered through all the cores, but they are rather more plentiful in the glacial marine zones. These grains, which range in diameter from about 0.1 to 1.0 millimeter and average 0.5 millimeter, have more or less frosted surfaces. They may have been derived from the reworking of glacial marine deposits or they may have been rafted by seaweeds. Little was done with the clay minerals other than to note that most of them have the optical properties of the beidellite or hydrous mica groups.

Six samples were tested with a 10-inch spectograph, which revealed the presence of appreciable amounts of barium and somewhat less of boron in each sample. All the samples gave negative tests for antimony, beryllium, bismuth, cadmium, ger- manium, lead, silver, tin, and zinc.

The original porosity of several samples in core 3 was calculated from the porosity of the dried samples. The original porosity plotted against depth in the core seems to indicate that fine-grained blue muds buried to a depth of 2 or 3 meters in the ocean floor are appreciably compacted.

Partial mechanical analyses of nearly 200 samples were made and plotted, but only four complete mechanical analyses were

made. The complete analyses were made by the sedimentation method and include four distinctive types of sediment.

Pumiceous fragments and smaller shards of basaltic volcanic glass (index of refraction near 1.60) are scattered throughout all the cores, but are somewhat more common east of the mid-At- lantic ridge than west of it. Unlike the alkalic volcanic ash it shows no conspicuous concentration in zones. Most of the basaltic glass and pumice has a thin surface alteration film of palagonite. The films are thickest on fragments in cores taken from ridges where oxygen-bearing waters had free access to the sediments. Two varieties of palagonite are recognized.

Core 11 represents only 34 centimeters of the sea floor because the core bit encountered deeply altered olivine basalt. About 15 centimeters of globigerina ooze rests on and within irregular cavities of the upper surface of a mass of clay that is apparently altered basalt. This clay is impregnated with manganese and contains nodular lumps of altered basalt. Part of the basalt near the base of the core is less altered. The clay contains scattered grains of sand and foraminiferal shells in which the original calcium carbonate has been replaced by a zeolite resembling phil- lipsite. This core may have penetrated the upper, deeply altered part of a submarine lava flow, but the evidence is not conclusive.

Core 10 contains two rather thick beds of distinctive clayey mud. About half of this mud is a beidellite or hydrous mica type of clay and the other half is made up of silt-size particles of basaltic glass, magnetite, augite, and calcic plagioclase. It contains very little common clastic material and exceedingly few Foraminifera. The composition and texture suggest that this mud was derived largely from a submarine volcanic eruption that threw into suspension clay particles perhaps partly from the normal sediment and from deeply altered basalt. A complete chemical analysis of this mud is given.

Foraminifera.—From these cores 184 samples representing every lithologic zone were examined for calcareous fossils. All but five samples contained Foraminifera. As in existing oceans deeper than several hundred meters, pelagic Foraminifera greatly outnumber the bottom-dwelling forms, though in variety of form and. in number of genera and species the bottom forms greatly exceed the pelagic. Several zones of relatively pure globigerina ooze were found, and many in which the ooze was clayey or sandy. Though variations in temperature were reflected by faunal changes, the general bathymetric facies of the faunas appear to be rather uniform throughout each core. The bottom faunas are least varied and prolific in cores from the deepest water, whereas in cores from the shallowest water they are by far the most varied and prolific. Cores from intermediate depths contain faunas of intermediate bathymetric facies. These relations to depth are, in general, characteristic also of faunas in the existing oceans. A few scattered specimens of Elphidium or Elphidiella were found. These genera thrive in shallow water, but in these cores the shells are so rare, so erratically distributed, and in some so poorly preserved that it seems probable they were rafted in by seaweeds or ice and therefore have no significance as indicators of depth. No species peculiar to the Miocene or Pliocene were found. It appears, therefore, that all the sediments penetrated by the cores are younger than Pliocene. Alternation of faunas that are characteristic of the warm and cold climates of the present day indicates great climatic changes during the time represented by these cores. The foraminiferal facies characteristic of cold and warm climates correlate with the alternating sequence of glacial-marine and warmer-water sediments indicated by the lithology. This correlation suggests that all the sediments in these cores are of Recent and Late Pleistocene age.

Diatomaceae.—Fifty-two species and varieties of diatoms were found in these cores. A large percentage of the species are neritic, warm-water forms that are foreign to the region today. Several

SUMMARY OF THE REPORT IX

alternations of warm-water and cold-water diatom floras occur in most of the cores, but their position in the cores is not in accord with the alternations of temperature inferred from lithology and foraminiferal facies. It is suggested that this disagree- ment may be due to the much longer settling time of the diatoms and that allowance should be made for it. The time equivalent of this difference of phase, as calculated from the vertical dis- placement necessary for the best approximation to agreement between the foraminiferal and lithologic data on the one hand and the diatom data on the other is of the order of 23,000 years. This figure appears absurdly high and a figure of several hundred years, based on extrapolation of experimentally timed settling in a relatively small vessel, is considered more reasonable. The action of cold and warm currents, some surficial and some deep seated, is suggested as the possible cause of the apparently erratic distribution of the diatoms. The possibility that the phase difference of 23,000 years mentioned above is related to shifts of ocean currents caused by advances and recessions of drift ice is offered as a speculation. Of 52 species and varieties illustrated, 2 species and 1 variety are described as new.

Ostracoda.—In preparing a series of samples from the cores for the study of the Foraminifera about 175 specimens of Ostracoda were f

X SUMMARY OF THE REPORT

Banks, where it seems to decrease about 25 percent in the first 1.5 meters. The organic matter content of the sediments tends to be greater in the warm zones, than in the cold zones, and in general it is slightly greater in sediments which, according to Cushman's determination of the Foraminifera, were probably deposited in areas in which the surface water was relatively warm. The organic content is rather closely related to the texture, and increases with increasing fineness of the sediments. The rate of deposition of organic matter is greater east of the mid-Atlantic ridge than west of it, presumably owing in part to a greater supply of plankton and in part to a slower rate of decomposition of the organic matter after it is laid down in the sediments. The slower rate of decomposition within the sediments is inferred from the greater state of reduction of the sediments, which is indicated by the nitrogen-reduction ratio. The nitrogen-reduction ratio suggests a slight increase in state of reduction with increasing depth of burial in the upper part of the deposits, but indicates no significant change in the lower part. The percentage of organic content tends to increase as the percentage of Foraminifera in the sediments decreases, but it shows no relationship to the calcium-carbonate content.

Selenium content and chemical analyses.—As a part of a comprehensive investigation of the distribution of selenium in marine

sediments and soils derived from them complete fusion analyses were made of 20 samples from the suite of 11 cores. These samples were taken from the tops of the cores and at intervale of approximately 1 and 2 meters below the top. In addition, 1 core taken on the continental shelf off Ocean City, Md., and 3 cores from the Bartlett Deep were sampled and analyzed, making a total of 31 analyses. The results of the analyses include all the normal analytical data obtained in a so-called complete soil analysis by the fusion method, and, in addition, determinations of organic matter, nitrogen, chlorine (in all but 12 analyses), hygroscopic water, and selenium. All the samples were analyzed with the entrained sea salts. The core from the continental shelf off Ocean City contained the most selenium—at the top 0.6 part per million, at 1 meter 1.0, and at 2 meters 2.0 parts per million. The samples from the North Atlantic cores showed a selenium content ranging from 0.06 to 0.8 part per million. Of the samples from the Bartlett Deep one contained 0.2 part per million of selenium, but all the others contained lees than 0.08 part per million. No evidence was found of a relation between the selenium content and volcanic activity.

The silica-sesquioxide and silica-alumina ratios are tabulated and their significance as means of comparing the analyses is discussed.

FOREWORD

By C. S. PIGGOT »

During the last cruise (1927-29) of the nonmagnetic ship Carnegie of the Department of Terrestrial Mag- netism of the Carnegie Institution of Washington a number of samples of the deep ocean bottom were obtained by means of the telegraph snapper. The Geophysical Laboratory determined the radium content of these samples and found that they contained a concentration of radium 2 as astonishingly high as that reported by Joly 3 and Pettersson 4 from similar samples taken by the Challenger and Princess Alice II. This high radium concentration in the surface layer of the oceato. bottom, which constitutes 72 percent of the surface of the globe, raises questions of great significance to both oceanography and geophysics. An obvious question is whether radium in so high a concentration is present down through all deep-sea sediments or only at the surface.5 If the first hypothesis is correct it indicates the presence of uranium throughout the sediments, whereas the second indicates the existence of radium itself, presumably separated out from the sea water. The study of this question requires samples of a type analogous to the cores so extensively used in sub- surface exploration on land. Inquiries among oceanographic organizations established the fact that although some cores a meter or more in length had been obtained from relatively shallow water, many of them were much distorted by the time they reached the laboratory, and none as long as 1 meter had been obtained from a depth of 4,000 meters or more.6 Those engaged in such research emphasized the need of apparatus capable of obtaining undistorted cores from great depths. In 1933 the Council of the Geological Society of America approved a grant for the development of such apparatus.7 For- tunately, cooperation was obtained from several special

i Geophysical Laboratory, Carnegie Institution of Washington.> Piggot, C. 8., Radium content of ocean-bottom sediments: Am. Jour. Sci., 5th

ser., vol. 25, pp. 229-238,1933.a Joly, J., On the radium content of deep-sea sediments: Philos. Mag., vol. 16, pp.

190-197,1908.4 Pettersson, Hans, Teneur en radium des depots de mer profonde: Resultats de

Campagnes Scientiflques par Albert I« Prince Souverain de Monaco, vol. 81,1930.« Piggot, C. S., op. cit., p. 233.* Since these inquiries were made D. Wolansky has published her review in the

Qeologlsche Rundschau (Band 24, Heft 6, p. 399,1933), in which she refers to the work of A. D. Archanguelsky in the Black Sea (Soc. Naturalistes Moscow Bull., new ser., vol. 35, pp. 264-281,1927). Wolansky mentions cores 3 to 4 meters long from depths of 2,237 meters. See also Wiss. Ergeb. Deutschen Atlantischen Exped. Meteor, 1925-27, Band 3, Teil 2, Lief. 1, pp. 4-28,1935.

' Piggot, C. S., Apparatus to secure core samples from the ocean bottom: Geol. Soc. America Bull., vol. 47, pp. 675-684,1936.

agencies, particularly the Burnside Laboratory of the E. I. du Pont de Nemours, whose ballistics expert, Dr. B. H. Mackey, offered fundamental suggestions and made many essential calculations and tests; also the United States Bureau of Lighthouses, from whose light- ship tender, the S. S. Orchid, many experimental soundings were made. Several forms of the apparatus were developed and tested, and in August 1936 14 satisfactory cores were obtained from the canyons in the continental shelf off New Jersey, Delaware, and Maryland, and another from the ocean floor below 2,500 meters of water.8 This first deep-sea test was made possible by the cooperation of the Woods Hole Oceanographic Institution and was carried out in connection with an investigation of the submarine canyons by H. C. Stetson of that institution. This test demonstrated the feasi- bility of the apparatus as built but suggested some minor changes in design. These were incorporated in another apparatus, which was put aboard the cable ship Lord Kelvin at Halifax, Nova Scotia. Through the courtesy of Mr. Newman Carlton, Chairman of the Board of Directors of the Western Union Telegraph Co., the Carnegie Institution of Washington was invited to have a member of its staff accompany the Lord Kelvin while that ship was engaged in making repairs to the North Atlantic cables, in order to test the apparatus in deep water. This offer was gladly accepted, and in May and June of 1936 I was on board the Lord Kelvin with the apparatus.

Because of the personal interest and cooperation of the commanding officer, Lt. Com dr. Bredin Delap, Royal Navy, retired, the undertaking was more suc- cessful than had been anticipated, and a suite of 11 excellent cores was obtained, extending from the Grand Banks of Newfoundland to the continental shelf southwest of Ireland.

All but two of these cores (Nos. 8 and 11) are more than 2.43 meters (8 feet) long, and all contain ample material for study. Of the two short cores, No. 8 was taken from the top of the Faraday Hills, as that part of the mid-Atlantic ridge is known, where the material is closely packed and more sandy and consequently more resistant; No. 11 came from a locality where the

• Cushman, J. A., Henbest, L. G., and Lohman, K. E., Notes on a core sample from the Atlantic Ocean bottom southeast of New York City: Geol. Soc. America Bull., vol. 48, pp. 1297-1306, 1937.

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XII FOREWORD

apparatus apparently landed on volcanic rock that may be part of a submarine lava flow. Soundings at the localities where the cores were taken show depths ranging from 1,280 meters at the top of the Faraday Hills to 4,820 meters in the deep water between the mid-Atlantic ridge and the continental shelf.

The thorough test made possible by the interested cooperation of everyone on board the Lord Kelvin fully demonstrated the capacity of the apparatus and pro- duced material from strata of oceanic sediments deeper than have ever before been available.

In order that this pioneer material might be examined to the best advantage and an adequate estimate made of the potentialities of cores of this type, a group of investigators representing various fields of science was invited to examine them. Efforts have been made to arrange the sequence of these investigations in such a way that the maximum information may be obtained with the minimum destruction of the samples.

The cores are now at the Geophysical Laboratory of the Carnegie Institution of Washington, where they and others that may be obtained by this laboratory will be held available for further research.

GENERAL INTRODUCTION

By W. H. BRADLEY

SIGNIFICANCE OF THE INVESTIGATION

The long cores of deep-sea sediment considered in this report represent a longer span of the earth's late geologic history, as recorded in abyssal sediments, than has been heretofore accessible. In a measure, therefore, this study has been exploratory. Because of that exploratory aspect we have not only presented the observa- tions but also have deliberately speculated upon various possible interpretations of the features observed in the cores and upon their relations with one another. Be- caus^e the cores are few in number and widely spaced, we offer many of the interpretations not as definite conclusions but rather as suggestions to be tested by whatever coring may be done in the future in that part of the North Atlantic.

From this investigation it appears that glacial marine deposits may prove to be sensitive indicators of the climatic changes that caused the growth and decay of continental ice sheets during the Pleistocene. In particular, it seems that the glacial marine record may throw light on the climatic fluctuations that determined substages of the Pleistocene. The marine record was the result of a continuously operating series of causes such that the deposits of each glacial substage were separated from one another by the deposits of the intervening warmer substage. The record of each substage has remained intact and was not obliterated by readvances of the ice. As the equatorward extent of the glacial marine deposits implies a corresponding expansion of continental ice sheets, the extent of the deposits may be used as a measure of the intensity of the climatic changes, and their thickness may be used as a rough indicator of the duration of glacial substages. Similarly, the thickness and poleward extent of tongues of nonglacial sediment—the foraminiferal marl—are measures of deglaciation. The area! extent of these tongues of sediment can be determined by additional cores taken at properly located stations.

When the glacial marine record is more fully known it should provide a basis for correlating the Pleistocene history of Europe and North America.

Cores taken along the meridians in series extending from the Arctic regions into the tropical parts of the- Atlantic should make it possible to map the southern limits of pack ice in the sea during successive glacial maxima, at least for the later part of the Pleistocene.

As the pelagic Foraminifera in these abyssal sediments are reliable indicators of surface-water temperatures in the Recent and Pleistocene epochs, it should be possible to trace southward into the tropics layers or beds of foraminiferal ooze that are the time equivalents of glacial marine zones. Such layers of foraminiferal ooze could then be correlated with the layer of globigerina ooze in the tropics that Schott 9 identified as a relatively cold-water, deposit that probably represents the last glacial epoch of the Pleistocene.

The study of climatology as well as geology may be advanced by the information to be derived from long sea-bottom cores. Significant evidence bearing on postglacial climatic changes may be obtained from minutely detailed study of the Foraminifera in cores taken in parts of the ocean where postglacial sedimentation has been comparatively rapid, as, for example, near the seaward edge of the blue-mud zone. On the assumption that such sediment accumulates at an essentially uniform rate, climatic fluctuations may be located approximately hi time within the postglacial interval and may be correlated from place to place along the ocean margins from the Arctic to temperate or even tropical latitudes and perhaps also from continent to continent.

Archeology, also, might profit from the knowledge of a relatively timed and correlated sequence of climatic changes, for such changes may well ha^e made a significant impress on the habits and migrations of peoples, particularly those that dwelt in regions where small changes in either temperature or rainfall were critical. As I have pointed out in an earlier paper, 10 students of archeology and early history, particularly in the Mediterranean region, might profit much from detailed studies of long cores of the sediment in the deep basins of the Mediterranean. In cores from that sea, as elsewhere, changes ID the foraminiferal faunas would indicate climatic changes, and the sediments would yield, in addition, evidence of volcanic eruptions and earthquakes. The time when the Sahara became a desert should also be recorded in the Mediterranean sediments by wind-blown sand. Such a change might conceivably be integrated with the wealth of archeo-

' Schott, W., Die Foraminiferen in dem aquatorialen Teil des Atlantischon Ozeans:. Wiss. Ergeb. Deutschen Atlantischen Exped. Meteor, 1925-27, Band 3, Teil 3, Lief. 1, pp. 120-128, 1935.

1° Bradley, W. H., Mediterranean sediments and Pleistocene sea levels: Science new ser., vol. 88, pp. 37C-379, 1938.

XIII

XIV GENEEAL INTRODUCTION

logical records of the region, and the later volcanic eruptions and earthquakes might be correlated with early history.

Some of the problems sketched so briefly here are touched upon in the several chapters of this report, but most of them must be left for future investigators. Nevertheless, methods by which such problems may be attacked are described and discussed at considerable length, particularly in the chapters on "Lithology and geologic interpretations" and "Foraminifera."

LOCATION OF THE CORE STATIONS

The cores were taken along a slightly irregular line between the easternmost part of the Newfoundland Banks and the banks off the southwest coast of Ireland, as shown in plate 1. Each core obtained by the Piggot coring device is numbered to correspond with the station number of the cable ship Lord Kelvin. Stations 1 and 2 were trial stations at which preliminary tests were made to familiarize the crew with the apparatus, and no cores were preserved. The 11 cores studied are numbered consecutively, 3 to 13. The relation between

M. N. Bramlette, J. A. Cushman, L. G. Henbest, K. E. Lohman, and P. D. Trask. As the biologic phase of the work progressed it became evident that other organisms than the foraminifers and diatoms should be studied. Accordingly Mr. Henbest invited Dr. Willis L. Tressler, of the University of Buffalo, to examine the ostracodes, Dr. Austin H. Clark of the United States National Msueum, to examine the echinoderms, and Dr. Harald A. Kehder, also of the United States National Museum, to examine the mollusks.

The organic matter content of the sediments was studied by Mr. Trask in collaboration with Messrs. H. Whitman Patnode, Jesse LeRoy Stimson, and John R. Gay, all members of the American Petroleum Institute.

As part of a comprehensive research project on the distribution of selenium in marine sediments and the soils derived from them Dr. H. G. Byers and Mr. Glen Edgington, of the Bureau of Chemistry and Soils, Uuited States Department of Agriculture, made complete chemical analyses of 20 samples from these deep- sea cores. These analyses, together with analyses of

w.ST. JOHNS

NEWFOUNDLAND Meters

5,000

MID-ATLANTIC RIDGE " FARADAY HILLS"

6 789

E.LANDS END

ENGLAND

FIGUBE 1.—Profile across the North Atlantic Ocean along the line of the numbered core stations shown on plate 1.

the core stations and the submarine topography is shown in figure 1, which is a profile along the dashed line in plate 1 that connects the stations and extends from St. Johns, Newfoundland, to Lands End, Eng- land. 11

TABLE 1.—Geographic location, length of the cores, and depth of the water from which they were taken

Core number

3—. ..—..„— .....................4— ...... ........... —__-—__-____5— ._—..-.. — _._.___..-.______.._.6— -—....__-_.___._.___..._„_...__7.— ..—..„— ............ .........8..— —_-___—.__._.___-.____..____9— .................... ..... ....10.... ................................11....................................12— .................................13— .................................

Depth of water (meters)

4,7003,9554,8204,1253,2501,2803,7454,1904,8203,2301,955

Length of core (meters)

2.812.712.822.902.621.242.769 07

.342.432.21

Lat. N.

46°03'00"48°29'00"48°38'00"J.Q°fWW49°32'00"49°36'00"49°40'00"A.QoAKff\(}ff48°38'00"49°37'00"AQO'iQ'nn"

Long. W.

jQOoq'Afl//

35°54'30"36°01'00"39°4d/*>ft"29°21'00"28°54'00"28°29'00"OQOQft'Qfi"17°09'00"

1 3o34/fW'IQOoC'fWV'

PERSONNEL AND COMPOSITION OF THE REPORT

At the request of Dr. C. S. Piggot, of the Geophysical Laboratory of the Carnegie Institution of Washington, the following six members of the United States Geo- logical Survey undertook a systematic study of the 11 deep-sea cores from the North Atlantic: W. H. Bradley,

11 Data for plate 1 and figure 1 were taken from International Hydrograpbic Bureau, Carte Generate Bathymfitrique des Oceans, 3d ed., sheets A-l and B-l, copies of which were furnished by the TJ. 8. Hydrographic Office.

samples from several other deep-sea cores and a discussion of the occurrence of selenium, are included in the chapter on "Selenium content and chemical analyses."

METHODS OF SAMPLING AND EXAMINATION

The Piggot coring device 12 takes the cores in brass sampling tubes that have an inside diameter of 4.9 cm. As soon as a core is taken, the tube is cut off at the approximate length of the core and sealed. The cores here discussed were opened under Dr. Piggot's direction at the Geophysical Laboratory of the Carnegie Institu- tion of Washington. A longitudinal cut was made along one side of each brass core barrel by means of a milling cutter so adjusted that it did not cut quite through the wall of the tube. The thin strip remaining was then ripped out without letting brass chips get into the core. After allowing the mud cores to dry somewhat, but not enough to shrink away from the tube walls, the cores and core barrels were cut in half longitudinally with a metal-cutting band saw. In this cutting, the milled slot was held uppermost so that the saw cut only the lower wall of the core barrel and threw the cuttings downward, away from the core.

» Piggot, C. 8., Apparatus to secure core samples from the ocean bottom: Qeol. Soc. America Bull, vol. 47, pp. 675-684,1936.

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LONGITUDINAL SECTIONS OF THE AIR-DRIED COKES.

Half of the core barrel was removed from core 11, but the core itself was not cut. Photograph by Geophysical Laboratory, Carnegie Institution of Washington.

GENEEAL INTRODUCTION XV

Each half core then remained undisturbed in its half cylinder cradle of brass core barrel. (See pi. 2.)

As several months elapsed between the time the cores were opened and the time this investigation began, the mud had dried thoroughly when Mr. K. E. Lohman took a succession of overlapping photographs of each core, about one fifth natural size. These photographs were then assembled as a key chart upon which were marked the parts from which samples for all phases of the investigation were taken. The dried segments of mud shifted somewhat from their original places each time samples were removed, though care was taken

to see that during sampling the segments kept their original order and orientation. By reference to this photographic key the findings of all the investigators have been correlated.

Most of the material was hard enough to be sawed into blocks with a hack saw, but a few of the most friable parts were sampled with small channel-shaped scoops of sheet metal after the loose material on the surface had been brushed away.

Samples for all phases of this investigation were taken from only one half of each core, the other half being held intact in the Geophysical Laboratory.

GEOLOGY AND BIOLOGY OF NORTH ATLANTIC DEEP-SEA CORES BETWEEN NEWFOUNDLAND AND IRELAND


By M. N. BEAMLETTE and W. H. BEADLEY

EXAMINATION AND ANALYSIS OF SAMPLES

Before sampling the deep-sea cores from the North Atlantic Ocean we made a record of the general aspect of the sediments, noting particularly the more obvious changes from one kind of sediment to another. These descriptive notes served as a guide in selecting the samples. As the combined length of the 11 cores is nearly 26 meters, a continuous sequence of samples 2 or 3 centimeters long would have necessitated the study of nearly 1,000 samples. With the time available it seemed preferable to take fewer samples and give them a more thorough examination than could be given so large a number. This decision was reached after the preliminary examination had shown that layers or zones of the mud penetrated were essentially uniform for considerable lengths of each core. Accordingly, the samples for the lithologic study were taken at intervals that averaged 10 to 12 centimeters, but the interval was varied from place to place in order to obtain samples representative of the obviously different lithologic types. (See pi. 3.)

Only one half of each core was used for sampling. Each sample for lithologic study was 2 or 3 centimeters long but included only part of the material, leaving the remainder at that place to be sampled for other phases of the work. Most of the individual samples represent sediment of a fairly uniform lithologic type, but the detailed examination showed that a few included sediment of two distinctly different types. Unfortunately, the samples sent to the chemical and hydrologic labora- tories for determination of total carbonate and for mechanical analysis were representative portions of whole samples, taken out before the significance of the various lithologic units was realized. Therefore, in the few samples that include two types of sediment the quantity of total carbonate and the mechanical analyses are not truly representative of either type. This is illustrated most strikingly by sample B-5S-59 from core 5. Microscopic examination showed that the upper part of this sample was distinctly different in composition and texture from the lower part. Had the two parts been analyzed separately the data plotted in

228324°—40——2

plate 3 would have shown a clear distinction between two lithologic zones rather than features that are intermediate between the two.

The samples were first examined under a binocular microscope, at which time the film of mud that had been smeared down along the walls of the core barrel as it penetrated the sediments was removed. In the few cores taken in places where the mud through which the core barrel passed was sticky, lumps and rolls of the sticky mud were carried downward below their normal stratigraphic position and squeezed into the core. Contamination of this sort, however, was easily recognized, and the contaminating mud was removed. In the examination of the samples under the binocular microscope the general lithologic type was noted, together with any evidence of bedding or other textural or structural features, such as borings. This examination also included estimates of the percentage of Foram- inifera and of recognizable inorganic constituents, such as zones of more abundant volcanic glass shards, pebbles and aggregates of tiny spherules of iron sulphide.

A little material scraped from a clean face of the sample was immersed in a liquid whose refractive index was 1.545, for examination under the petrographic microscope, and the relative abundance of the finer organic and inorganic constituents was estimated. These constituents included the diatoms and other siliceous organisms and the minute calcareous algae belonging to the Coccolithophoridae. Accurate determination of the amounts of these constituents would have required a great deal more time than seemed warranted. The relative accuracy of these estimates is considered under the heading "Carbonante content of the sediments."

The samples were next submitted to the chemical laboratory of the Geological Survey, where E. T. Erickson determined the approximate content of total carbonate in all samples by treating them with hot dilute hydrochloric acid until the solution was slightly acid as indicated by methyl orange. This procedure, though rather crude, was adopted for its speed, so that many samples could be tested. The results are subject to errors of several percent.

1

GEOLOGY AND BIOLOGY OF NORTH ATLANTIC DEEP-SEA CORES

In samples taken near the top, middle, and bottom of each core Erickson also determined quantitatively the MgO, CaO, and MnO in a representative part of each sample. The insoluble residues from each of the samples were then wet-screened for mechanical analysis in the hydrology laboratory of the Geological Survey, under the direction of C. S. Howard. Before screen- ing they were shaken in a mechanical agitator for about 4 hours with a comparatively large volume of distilled water, to which had been added a small quantity of dilute sodium oxalate solution. Like the carbonate determinations, these mechanical analyses are only approximations, owing largely to the difficulty of dis- persing the sediment that had been treated with acid and thoroughly dried.

The screened fractions were then examined microscopically for a closer estimate of the proportions of certain noncalcareous constituents, such as volcanic ash and siliceous organisms. In this examination the rather large percentages of clay aggregates in the sand- size fractions, obviously the result of incomplete dis- integration of some of the more clayey samples, were also estimated, in order to correct the mechanical analyses, the results of which are plotted in plate 3.

This examination revealed the need of supplementary data from certain parts of the cores between samples; accordingly, additional samples were taken and sub- jected to the same tests, and the results were also plotted in plr.je 3. Much of the material between samples was then examined for a few particular features, in order to delimit the zones of volcanic glass shards and zones of glacial marine deposits and also to make certain that no zones of volcanic material had been missed.

ACKNOWLEDGMENTS

In the preparation of this chapter on the lithology and physical geology of the cores we have had the benefit of discussion with many of our colleagues in the Geological Survey and with various members of the Geophysical Laboratory of the Carnegie Institution. Acknowledgment is made at appropriate places in the text for analyses and tests made for several phases of the investigation, and we wish to express here our thanks to C. S. Howard, of the hydrology laboratory, and R. C. Wells and George Steiger, of the chemical laboratory, for their ready cooperation and for the laboratory space and facilities which, to their own inconvenience, they generously placed at our disposal.

PRESENTATION OF DATA

Many of the data obtained from the investigations outlined above are presented graphically in plate 3 to facilitate general comparison, although the variations of any one constituent are somewhat less easily followed in so comprehensive a diagram. The boundary between material of silt size and sand size as used in this

report is 0.074 millimeter, instead of the 0.0625 millimeter commonly accepted as the upper size limit of silt, because, of the sieves available, the one having openings of 0.074 millimeter was the nearest. Like- wise, the boundary between sand size and coarse sand size was taken as 0.59 millimeter, rather than the generally accepted 0.5 millimeter, because 0.59 millimeter was the nearest sieve size available. The proportion of coarse sand in the sand-size fraction of the sample seemed significant enough to be indicated on the diagram, but the difficulty of showing effectively small percentages necessitated special plotting. Conse- quently, the percentage of coarse sand in the sand-size fraction of each sample is plotted in a separate column to the right of the column representing the core. The right-hand column shows also samples that contain one or more pebbles 3 millimeters or more in mean diameter. In view of the apparent significance of these pebbles, it is unfortunate that the data are not adequate to show their relative abundance. In the course of sampling it became evident that only samples from cores of diameter much larger than the ones available could show the true quantitative distribution of pebbles as large as these, therefore no attempt was made to show in plate 3 whether the sample contained one or several. Supple- mentary examination of the whole cores, however, indicated that adequate data on their distribution in the cores would show more clearly their zones of occurrence hi the sediments. .

The column representing the core samples shows also the relative abundance of Foraminifera and of coccoliths, both of which are discussed further in connection with the carbonate content of the sediments. (See pp. 17-21.) The coccoliths are minute calcareous plates, most of which are between 0.002 and 0.015 millimeter in diameter. The symbol "common" means that they are numerous, though by reason of their small size they make up roughly only about 1 percent of the whole sample; "abundant" indicates that they make up about 5 percent or more of the sample. Even where most abundant, however, they probably do not make up more than 10 percent of the sediment.

The lines between cores shown in plate 3 indicate the correlation of zones of distinctive sediment. The evidence upon which these zones are distinguished and correlated is given below in considerable detail, together with interpretations of their significance.

STRATIGRAPHIC UNITS

VOLCANIC ASH ZONES

Shards of volcanic glass are rather abundant hi the upper part of most of the cores and are sufficiently plentiful to characterize a zone. This upper volcanic ash zone is indicated in plate 3 by the uppermost stippled zone. The volcanic ash is abundant only in the lower part of the zone, and the base of the zone is rather sharply delimited. Above the base of the zone

PAET 1. LITHOLOGY AND GEOLOGIC INTERPRETATIONS

the shards rapidly decrease in abundance upward, though they are sparsely scattered through the sediment to the top of each core. The ash consists of unaltered vitric shards that have an index of refraction near 1.51, which suggests that the glass is of alkalic or calc-alkalic composition. The characteristic form of the shards makes all but the finest grains recognizable, even under the binocular miscroscope. A reex- amination of material from this ash zone, including samples intermediate between those represented in plate 3, showed that near the base of the upper ash zone in most of the cores there are generally several thin layers in, which the ash is distinctly more abundant or, in some samples, forms the dominant constituent; but between these more or less distinct layers shards are mixed with a greater proportion of other sediment. In cores 7 and 9 the ash is not concentrated in distinct layers and the only marked difference is the increase in abundance downward to the well-defined base of the zone. The apparent significance of this scattered distribution of the shards within the zone of volcanic ash is considered under the headings "Evidence of bottom currents" and "Role of mud-feeding organisms." (See pp. 14-15, 22-23.)

Although volcanic ash is the dominant constituent, in some of the ill-defined layers one to several millimeters thick, it rarely makes up more than 5 percent of the total sediment in an ordinary sample 2 to 3 centimeters long from the upper ash zone, and it averages nearer 1 percent. In the noncalcareous residues of these samples, however, the volcanic ash commonly makes up about 25 percent of the sand-size material and is therefore a distinguishing feature of this zone. In the upper ash zone the volcanic ash is present in greatest concentration in core 9, and there also the concentration is greatest in the lower part of the zone. Much of the scattered ash in the upper part of the zone in this core may represent contributions winnowed from the sediment on nearby areas of much shallower water. (See p. 14.)

A correlation of this upper ash zone from one core to another is suggested in plate 3, and though this correlation appears to be somewhat less certain in core 8 on the mid-Atlantic ridge and thence eastward, other lines of evidence, considered on page 6, seem to confirm the interpretation indicated.

Cores 4 to 7, on the west side of the mid-Atlantic ridge, penetrated a lower zone of volcanic ash, which is similar to the upper one. In the lower zone, the vitric shards, as in the upper zone, have a refractive index of 1.51 and are scattered through the zone rather than occurring in one or more sharply defined layers. The lower zone differs from the upper one in commonly having smaller shards and fewer of them. Reasons for the failure to find this lower ash zone in core 8, and in any of the cores east of the mid-Atlantic ridge are considered on page 6, where the correlations are discussed.

An occasional shard of volcanic glass having a refractive index of 1.51 was found in several samples between the upper and lower ash zones. Because these stray shards are so rare it seems probable that they were reworked from the lower ash zone up to their present positions by mud-feeding organisms or that they were derived from nearby mounds or ridges on the sea floor where the lower ash zone is exposed to the action of gentle currents. (See pp. 14-15.) The stray shards, however, are most common in samples B-53 and B-55 of core 5 and in sample B-214 of core 12. Taken alone, the relative abundance of volcanic ash in these samples suggests the existence of other ash zones, comparable to those just described though thinner and with a lower percentage of volcanic material. An unusual significance attaches to these three samples, however, for reasons other than their content of volcanic ash. The layers that they represent have unusually sharp bound- aries at both base and top, they contain relatively little of the usual fine-grained constituents, and they have other distinctive physical characteristics, all of which suggest that they resulted from submarine slumping. These anomalous samples are considered more fully under the heading "Submarine slumping" (pp. 15-16).

The similarity of the alkalic glass shards to ash from explosive volcanic eruptions and the distribution of the shards in the upper and lower ash zones suggest that each of these zones represents an accumulation of normal volcanic ash that was transported through the air out over- the ocean. No progressive increase in either the amount or grain size of the pyroclastic material in a particular direction was detected, but original variations of this sort may well have been obscured by the local variations believed to be due to redistribution of the shards.

The source of the alkalic glass shards in these cores is unknown. Geologically recent eruptions in the Azores include trachytic as well as ferromagnesian materials, and possibly the ash may have come from there. Alkalic volcanic rocks are associated with the basaltic volcanics of Iceland and Jan Mayen and, according to Peacock, 1 some of the volcanic activity in Iceland occurred during Pleistocene and post-Pleisto- cene time. The volcanoes of these northern islands that expelled the more silicic material may have been the source of the ash that characterizes the zones of volcanic ash in the cores.

GLACIAL MARINE DEPOSITS

From a little below the base of the upper volcanic ash zone downward for a short distance, most of the cores show a decrease in the amount of calcium carbonate and a corresponding decrease in the number of both Foraminifera and coccoliths, which are the dominant calcareous organisms. (See pi. 3.) As these limy

1 Peacock, M. A., Geology of ViSey, southwest Iceland: A record of igneous activity in glacial times: Royal Soc. Edinburgh Trans., vol. 54, pp. 441-465, 1925-1926.

GEOLOGY AND BIOLOGY OP NORTH ATLANTIC DEEP-SEA CORES

constituents decrease the clastic sediment increases cor- respondingly and is marked particularly by a greater content of coarse sand, granules, and pebbles. The granules and pebbles range in diameter from several millimeters to more than a centimeter. Most of them are somewhat rounded, but some are angular. They represent a wide variet}^ of rock types, of which limestone is the most abundant; but various types of dark- colored shale, mudstone, sandstone, and gueissic and schistose rocks are also common. Less common are granules and pebbles of dolerite, granodioritc, quartzite, granulite, chert, and probably other rocks.

The size of these rock grains and the wide range of lithologic types that are representative of continental rocks rather than rocks of volcanic islands lead us to believe that their occurrence in these deep-sea sediments, far from land, means that they were transported by drifting ice. The same explanation has been given to account for the many pebbles, cobbles, and boulders that have been dredged from different parts of the North Atlantic. Peach 2 and Flett 3 have given detailed descriptions of some of the pebbles and boulders found in the dredgings. Some of the larger pebbles and cobbles have facets and striated surfaces like the cobbles found in glacial moraines. Their transportation to deep parts of the ocean remote from land, seems to be reasonably explained only by the assumption that they were carried by drifting ice. Cobbles of this sort have been dredged from the ocean floor as far south as the Azores 4 and at stations north of Madeira,5 which suggests that they were transported by floating ice during the Pleisto- cene, when glaciers filled the Irish Sea and extended out over large areas of the continental platform into the North Atlantic.

The large amount of rock debris that may be transported by drifting icebergs, particularly those from glaciers and inland ice, as contrasted with drifting shelf ice, is suggested by Tarr's statement,6 "There are thousands of tons of boulders, gravel, and clay sent into the sea from the front of the Cornell glacier every year, and much of this passes beyond the fjord out into Baffin Bay." Pratje 7 reported that icebergs from land ice in the South Atlantic have been found to carry as much as 16 cubic centimeters of sediment per liter of ice, or about 1% percent by volume.

2 Peach, B. N., Report on rock specimens dredged by the Michael Sars in 1910, by H. M. S. 1 riton in 1882, and by H. M. S. Knight Errant in 1880: Royal Soc. Edinburgh Proc., vol. 32, pp. 262-288,1913.

3 Flett, J. S., Report on the rock specimens and some of the oozes collected by the S. S. Faraday and S. S. Minia from the bed of the North Atlantic in 1903, in Murray, Sir John, and Peake, R. E., On recent contributions to our knowledge of the floor of the North Atlantic Ocean: Royal Geog. Soc., Extra Pub., pp. 23-30,1904.

4 Andrge, K., Die Geologie des Meeresbodens, p. 294, Leipzig, 1920. «Idem, p. 379.6 Tarr, R. S., The Arctic sea ice as a geological agent: Am. Jour. Sci., 4th ser., vol. 3,

p. 228, 1897.7 Pratje, O., Bericht fiber die geologische Arbeiten der deutschen atlantischen Exp.

Metsor: Gesell. Erdkunde Berlin Zeitschr., 1926, p. 257.

Philippi's study 8 of the bottom sediments from the Antarctic collected by the Gauss, in part by coring and in part by dredging, helps greatly to explain analogous sediments in the North Atlantic cores. The sediments adjacent to the ice front in Antarctica contain little calcium carbonate but consist dominantly of clastic material, including coarse sand and pebbles of various metamorphic and igneous rocks. The fraction of finer sediments consists of silt rather than the clayey material that is typical of the common oceanic blue mud. These sediments, which Philippi appropriately named "glacial marine deposits," apparently extend northward only about as far as the northern limit of pack ice. Core samples froiri farther north, however, revealed the highly significant fact that these glacial marine deposits extend northward beneath the diatom ooze that is forming today in a wide belt north of the pack ice. Cores from yet farther north contained glacial marine deposits below a layer of globigerina ooze, which is the kind of sediment accumulating today in that part of the ocean north of the area of diatom ooze. The diatom and globigerina oozes cover the glacial marine deposits to a depth of 10 to 20 centimeters. The glacial marine deposits now being formed in the region of pack ice led Philippi to believe that the similar deposits farther north were deposited during the Pleistocene epoch, when the ice front was much farther north. He also suggested 9 that the downward decrease in calcium carbonate, commonly observed in cores of ocean-bottom sediments a meter or less in length, even in the equatorial Atlantic, reflects a climatic control and that the lesser quantity of calcium carbonate is a consequence of the colder water during the Pleistocene.

The zone of sediment underlying the upper ash zone in our North Atlantic cores (see pi. 3) is so similar to the glacial marine deposits of Philippi that it is interpreted as a glacial marine deposit of the last glacial stage of the Pleistocene. This interpretation is con- firmed by Cushman and Henbest (see pi. 4), who conclude from their study of the foraminiferal faunas that this zone is characterized by a pelagic fauna from colder water than that of the overlying globigerina ooze. Below the glacial marine zone just described we found in some of our cores, particularly cores 4 to 7, which were taken west of the mid-Atlantic ridge, an alternating sequence of glacial marine zones and zones of sediment resembling rather closely those forming today in that part of the ocean. All these glacial marine zones have the distinctive features that have already been described— namely, the pebbles, the coarse sand, the relatively

8 Philippi, E., Die Grundproben der deutschen Sudpolar-Expedition, in Von Drygalski, E., Deutsche Sudpolar-Expedition 1901-1903, Band 2, Heft 6, pp. 431-434, 1912.

9 Philippi, E., tiber das Problem der Schichtung und fiber Schichtbildung am Boden der heutigen Meere: Deutsche geol. Gesell. Zeitscbr., vol. 60, pp. 346-377, 1908.

GEOLOGICAL SURVEYPROFESSIONAL PAPER 186 PLATE 8

Lat. 46°03'00"N.Long.43°23'00"W.Depth 4700meters

3

Lat. 48°29'00"N. Long.35°54'30"W. Depth 3,955 meters

4

Lat. 48°38'00"N.Long. 36° 01'00" W.Depth 4820meters

5

Lat 4go03'30"N. Long.32°441 30"W. Depth 4,125 meters

6

Lat. 49°32'00"N. Long. 29° 21' 00"W- Depth 21250 meters

7

FARADAY HILLS Lat. 49°36'00BN. Long. 28°54'OOW. Depth 1,279 meters

8

Lat. 49°40'00"N. Long. 28°29'OOW. Depth 3,745 meters

9

Lat. 49°45'00N N.Long. 23030'30"W.Depth 4,190 meters

10

Lat. 48°381 00"N. Long. I7°09'00"W. Depth 4,820 meters

B-2

B-3

B-4

B-5

v-a[EW-3B-6

B-7

B-8

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B-13

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B-73

B-74

B-75

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B-102

Lat. 49°37'00"N. Long. I3°34'00"W. Depth 3,230 meters

12

Lat. 49WOO"N. Long, is-as'ocrw.Depth 1,955 meters

13

W-18

Sample taken from the anchor flukes at the site of core IO.

Sample taken from the water- exit ports of the coring device.

QIIIIII] Percentage of total carbonate

-i——r--i Percentage of clay and silt J——'-J (Iess than 0.074mm.).

Percentage of material of sand size or larger (greater than 0.074mm.).

Width of column represents total amount of material of sand size in sample. Length of bar represents percentage of coarse sand (larger than 0.59mm.). Large dot at end of bar Indicates presence of one or more pebbles 3mm. or more in mean diameter.

Percentage of Fbraminifera (indicated by the distance of the dotted line from the left side of the column).

Coccoliths abundant.

Coccoliths common.

Both samples are parts of strata • that lie stratigraphically higher

than the top of core 10.

B-227

^^•iii^ Zone of alkalic volcanic glass shards.Ks'iV-' iiV-i-Jt sl/li'l

Zone of glacial marine deposits.

DIAGRAM SHOWING THE CORRELATION OF THE LITHOLOGIC ZONES IN THE CORES.Each core is represented by two vertical columns. The patterned rectangular blocks in each left-hand column represent samples that were taken for routine mechanical and

chemical analyse* and microscopic examination. The parts of the core* from which namf.len were taken for special purposes or supplemental examination are indicate 1 by braces. The samples are numbered in two series distinguished by the prefix letters B and W. The width of each column is taken to represent 100 percent by weight of the sediment, and the horizontal length of each pattern within a sample block represents the percentage of the constituent. The left-hand column nhows the percentage of carbonate, clay and silt, sand, and Foraminifera and the relative abundance of Coccoliths. The right-hand column indicates the percentage of coarse sand and the presence of pebble*.

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small percentage of calcium carbonate, the small number of Foraminifera, and the virtual absence of coccoliths. They have other features characteristic of the glacial marine deposits, such as a smaller quantity of clay, which is evident from the texture and the smaller shrinkage of the air-dried samples, and, locally at least, a lumpy structure, which appears to represent ellipsoidal or tubular borings that were subsequently filled with the adjacent mud to form coprolite-like pellets. Some of the pellets are as much as a centimeter hi diameter. Whether these are coprolites or mud-filled borings of molluscs, worms, or some other organism is not known, and the significance of their occurrence in the glacial marine deposits in greater abundance than in other sediments is not apparent.

Schott's recent study 10 of the Foraminifera in the cores from the equatorial Atlantic collected by the Meteor expedition led to a similar interpretation of Pleistocene and post-Pleistocene deposits in that part of the ocean. His interpretation was based only on the ecology of the Foraminifera, as the sediments of that part of the Atlantic showed no accumulations of ice-rafted sand and pebbles. The cores, which averaged less than a meter hi length, were sampled in the upper, middle, and lower parts. They showed a surface layer containing a warm-water fauna, a lower layer containing a cold-water fauna, and some of the longest cores showed a still lower layer containing a warm- water fauna. In the two layers that indicated a warm-water environment the Foraminifera were essentially like those living today in that part of the ocean. Schott interpreted the intermediate layer, that layer representing a cold-water environment, which in most places contained less calcium carbonate, as a deposit formed during the latest Pleistocene glacial stage; the lowest layer as a deposit of the last interglacial stage; and the uppermost layer as a post-Pleistocene deposit.

The correlation of the glacial marine zones and other distinctive zones that we found in our North Atlantic cores is discussed below, together with an interpretation of their significance.

CORRELATION OF ZONES REPRESENTED IN THE CORES

Layers or zones of alkalic volcanic ash hi general are reliable for use in correlating strata because this kind of ash is erupted from volcanos of the explosive type and is distributed widely in the air. It must therefore accu- mulate on the sea floor at essentially the same time throughout the extent of its dispersal. When such ash zones are parts of a sequence of distinctive beds and the sequence is repeated at the several localities between which strata are to be correlated the reliability of the ash zones is further enhanced. As indicated in plate 3, cores 4, 5, 6, and 7 contain two ash zones and have the

'« Schott, W., DieForaminiferen in dem aquatorialen Teil des Atlantischen Ozeans: Wiss. Ergeb. Deutschen Atlantischen Exped. Meteor, 1925-27, Band 3, Teil 3, Lief, 1, pp. 120-130, 1935.

same sequence of glacial marine deposits between the ash zones. Below the lower ash zone in each core there is another glacial marine zone, which is underlain by foraminiferal marl similar to that found today at the surface of the ocean floor. The sequence of zones in these four cores agrees so well that their correlation seems well established in this area west of the mid- Atlantic ridge.

Core 3 is markedly different, as might be expected from its position within the area of terrigenous mud, or blue mud, near the Newfoundland Bank. This core consists of a remarkably uniform calcareous mud. Three thin and rather widely spaced layers of less limy mud and one thin silty layer near the bottom mark the only departures from the apparent homogeneity of this core. Small shards of alkalic volcanic ash like those in the ash zones of the other cores are very sparsely dis- seminated throughout this core but are not concentrated in any zone. The sediment of this core contains only an insignificant amount of sand-size clastic grains and no zones of coarse sand and pebbles, such as are found in the glacial marine zones of the other cores. The interpretation by Cushman and Henbest of the Foraminifera in this core (see pi. 4) is that the surface- water temperature was nearly uniform while the sediments represented by the core were accumulating, except for the three thin clay zones. The pelagic Foraminifera hi the clay zones indicate colder water. Despite these thin cold-water zones, the distribution of the volcanic ash shards and the absence of sand and pebble zones lead us to believe that this core represents only sediments of post-Pleistocene time that accumulated in an area where the rate of sedimentation was more rapid than at the sites of the other cores. A core of greater length from this locality would be of particular interest to check this interpretation and give a basis for comparison of the post-Pleistocene rate of accumulation at this station with the rate at other core stations.

Core 3 contains no coarse sand and not even a single pebble, a fact that seems at first somewhat surprising, because this is the only one of the 11 cores that comes from within the present usual limits of drift ice. (See pi. 1.) However, the investigations of a number of explorers, notably Boggild and Nansen,have shown that much of the floor of the Arctic Ocean well within the limits of drift ice is covered with a deposit made up only of silt and clay that is free from sand and pebbles. 11 The explanation seems to be that even the berg ice in the Arctic and North Atlantic now contains but little clastic material, and apparently much of that little is dropped between Greenland and North America before it reaches the region south and southeast of the New- foundland Banks. During the glacial epochs, however, the continental glaciers presumably furnished

" Andree, K., Geologic des Meeresbodens, pp. 378-379, 469-475, Berlin, Gebrflder Borntraegcr, 1920.

6 GEOLOGY AND BIOLuGY OF NOETH ATLANTIC DEEP-SEA CORES

many more bergs, and these bergs carried much clastic debris into the ocean.

Core 8, which was taken in 1,280 meters (700 fathoms) of water on the Faraday Hills part of the mid-Atlantic ridge, does not show the well-defined sequence of zones noted in cores 4 to 7, consequently its correlation with them is rather uncertain. The sediments throughout this core consist largely of sand and sand-size calcareous organisms, and the proportion of fine-grained material is so small that the dry core is friable. As is discussed later under the heading "Evidence of bottom currents" (pp.14-15) the sediment at this place seems to have accumulated where currents moved over the ridge with sufficient velocity to winnow out most of the finer constituents. As a result of this selective process the upper ash zone in core 8 contains comparatively few shards, but these are large and thick. Shards were found as far down as the top of sample B-131, which is therefore taken as the base of the upper ash zone. Because the shards are less numerous and the zone less well defined than in other cores, the correlation line at the bottom of the upper ash zone is indicated in plate 3 as doubtful. Although other lines of evidence make it seem probably that core 8 penetrated deep enough to have passed through the lower ash zone, no ash was found. Inas- much as the shards in this lower zone are generally finer and less abundant than those in the upper ash zone, it is possible that they may all have been winnowed out, as have most of the shards hi the upper zone, so that no trace remains at this site. The glacial marine zones are likewise less surely identifiable in this core, for the reason that the coarser sand and pebbles characteristic of the glacial marine deposits are less distinctly concentrated at definite horizons, perhaps because they have been more reworked and mixed with interglacial and postglacial sediments. Correlation of the glacial zones in core 8 with those in the other cores is therefore unsatisfactory, and this uncertainty is indicated in the correlation lines shown in plate 3.

Core 9 contains an exceptional abundance of volcanic ash in the middle part, and shards are scattered rather sparsely through it from the middle to the top. The distribution of the ash inclines us to believe that this ash zone corresponds with the upper ash zone of the cores west of the mid-Atlantic ridge. This belief is strengthened by the absence of coarse-grained material of the glacial marine type, either scattered or in beds, within the ash zone, and by the occurrence of a well- defined glacial marine zone a short distance beneath the base of the ash. The unusual concentration of thin, delicate volcanic glass shards in this core and the unusual abundance of other fine-grained constituents such as diatoms, coccoliths, and clay-size particles are discussed more fully on page 14.

The correlation of core 10 with the others is somewhat unsatisfactory for two reasons—first, the coring device penetrated deeper than the length of the core

barrel, so that an unknown amount of sediment was lost through the water ports above the top of the core barrel; and second, at this station there are two rather thick beds of an extraordinary type of mud not represented in any of the other cores. At the time this core was taken Piggot collected some of the mud that had come out of the top of the core barrel and lodged in the water-exit ports. This sample (W-18) was of the same peculiar mud that makes up the uppermost quarter of the core, but it contained a moderate quantity of small pebbles and coarse sand. Piggot also collected, at this same station, a sample (W-17) of the globigerina ooze that stuck to the anchor flukes. Thus we know that at this station globigerina ooze blankets the sea floor, as it does at all the other stations except No. 3. Apparently all of the layer of globigerina ooze, the thickness of which is unknown, and some of the peculiar mud that makes up the top of core 10 was lost through the water ports. Nevertheless, it seems probable that the volcanic ash zone in this core is the upper ash zone of the other cores because of the abundance and general coarseness of the shards; because the shards continue upward, though sparsely, to the top of the core; because they were found also in the globigerina ooze above; and because there is a relatively thick glacial marine zone just below the base of the ash. The coarse sand and pebbles in the mud a little above the top of this core might be interpreted as material dropped from a stray iceberg as are other scattered or isolated pebbles found outside the glacial marine zones in the other cores. However, as this particular sample came from a disturbed core, not too much significance can be attached to its peculiarities.

Core 11 struck hard volcanic rock before penetrating any of the recognizable zones used in correlating the cores. This rock was hard enough to bend the core bit and stop it after it had penetrated the sediments for only about 34 centimeters. The thin deposit of globigerina ooze overlying the rock contains no shards of alkalic glass such as are scattered through the other cores, sparingly but continuously